THIS invention relates to a tool insert.
The use of diamond compacts, also known as PCD, as cutting elements are well known in the art and used extensively in various cutting, drilling, milling and other abrasive operations due to the high abrasion resistant properties of diamond cutters. The diamond cutters, however, are not always suitable for all substrates encountered. For instance, it is well established that diamond cutters cannot be used satisfactorily for milling or drilling through ferrous substrates such as steel. As a result, the use of diamond cutters in certain down the hole drilling operations is not suitable as milling through a steel casing, which is used to line the vertical borehole or shaft, is required.
As PCD is not suitable for drilling through the steel casing due to reactions with the ferrous materials, an alternative drill bit insert is required. Accordingly, tungsten carbide cutters are typically used in the drill bit to mill through the steel casing. Once through the casing, the tungsten carbide inserts have to be replaced with abrasive resistant cutters such as diamond cutters in order to drill into the bedrock. This means that the drill bit has to be removed and replaced with an appropriate bit. As the drill strings that have to be removed are very long, this is a time consuming exercise that results in costly downtime.